Patent GB-707221-A (GB)
Title: Improvements in or relating to automatic telecommunication exchange systems
IPC: H04Q3/00
Filed: 1950-01-16
Abstract: 707,221. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. (Hertog, M. den). Jan. 12, 1951 [Jan. 16, 1950], No. 1095/50. Class 40 (4)  In an automatic exchange comprising a group of selector switches at a selector stage which are controlled both as regards the selection of outlets and the setting of the switches to the selected outlets by means of a common control circuit, the arrangement is such that the common control circuit can control the setting of a switch to a' selected outlet and simultaneously control the selection of an outlet or outlets for one or more other switches. Specification 700,089 is referred to. General operation.-Fig. 1. A scanning circuit in the common control circuit of a group of selectors is permanently available for signalling the availability of all outlets from the selectors to all register-controllers associated with the selectors, regardless of whether the common control circuit is also in use for causing the setting of one of the selectors in accordance with a selection already made by its associated register-controller. As shown, register-controllers REA, REB control connections via selectors SEA, SEB respectively, and for each free outlet the scanning circuit (explorer 1) transmits an impulse in a characteristic time position in its scanning cycle over the d wires to the register-controllers. These impulses are compared by each of the registercontrollers with a locally supplied impulse characteristic of its wanted group of outlets, and if the impulses coincide the comparator C passes an impulse via regenerator IG to the register R to record by its time position the outlet selected. The register-controller then tests the common control circuit for availability for selector operating and, if it is idle, seizes and busies it for this purpose. The identity of the selected outlet is transferred to the common control circuit in the form of a time position pulse over the c wire, after which the horizontal magnet HAM or HBM is operated changing over the associated contacts. The other register-controller remains connected to wires VI, III and V and continues to search for a free outlet in its wanted group, recording such an outlet when found. It can hold this record for approximately 300 m.s. during which time it seizes the common control circuit should it become free. At the end of this time if the common control circuit is still busy the record is cancelled and searching recommences. Type of selector used.-The system operates in a similar manner to that disclosed in Specification 700,088 but differs in details. The switches used are cross-bar multi-switches of the general type described in that Specification. A multi-switch comprises as many horizontal bars as there are individual selectors in the multi-switch and half as many vertical bars as there are outlets. At each intersection of the horizontal and vertical bars there is a contact pusher which by forward or backward movement brings the inlet corresponding to the horizontal bar into contact with one or other of the two outlets corresponding to the vertical bar. The 50 vertical bars for the 100 outlets are arranged in 25 pairs, a 26th pair being provided for routine testing if desired. The selection of a vertical bar is controlled by the operation of one of 25 vertical magnets VM (Fig. 5), each associated with a pair of bars. and the operation of one of two common vertical servo-magnets SVMA, SVMB which chooses one bar of the pair. The horizontal bar to be operated is indicated by the operation of its individual horizontal magnet HM (Fig. 4) and it is then moved'either to the right or to the left by one of the two common horizontal servo-magnets SHMA, SHMB thus causing the contact pusher to move forwards or backwards to select the contact set to be operated by the bar. The vertical magnet and the vertical and horizontal servo-magnets are then released, whereupon the vertical bar drops back but the operated horizontal magnet holds the horizontal bar locked to maintain the contacts closed. The outlets are arranged in four rows, consisting of outlets 00-24, 25-49, 50-74 and 75-99 respectively, and each vertical magnet corresponds to one outlet in each row. SVMA lifts the vertical bars of outlets in the first two rows and SVMB those in the last two rows. SHMA causes a contact set to be closed in row 1 or 3, and SHMB one in row 2 or 4. The outlets may be distributed as desired in any number of groups to a maximum of ten. Operation.-It is assumed that the digits of the wanted number have been registered in the register-controller (Fig. 2) in any well known manner (not illustrated) and that the first group selector (Fig. 4) has been connected up over wires a, b, c, d. The ground applied to wire b by back OK (Fig. 2) brings up GA (Fig. 4) over a back contact of the horizontal bar of the selector, whereupon the common control circuit is connected to wires a, 'c and d. Ground on wire I operates GB (Fig. 5) which connects ground to the anodes of cold cathode tubes VRA, VBB, VRC. A resistance Rg (Fig. 5) is provided for each outlet and is connected' to the corresponding wire e<SP>1</SP> (Fig. 4) of the next selection stage where, if the outlet is idle, it is connected to negative battery over back GA. If the outlet is busy, wire e<SP>1</SP> is grounded over front GA in the preceding selector (Fig. 4). The other ends of the resistances Rg are connected to a scanner similar to that of Specification 700,088, which is controlled by pulse sources Pa ... Pc (Fig. 8) so that the paths from the resistances Rg to the grid of tube ET1 are enabled cyclically in turn. In each case the gate DRCP (Fig. 5) is connected to a source of pulses Pd (Fig. 8) which characterizes the group to which the outlet belongs. The sources P are normally relatively positive but are relatively negative during the impulse period so that each gate disables the corresponding path except when the associated source is transmitting an impulse. Therefore the tube ET1 receives impulses during the first cycle of 100 time positions in respect of only those outlets to which source Pdl is connected, i.e. those in group 1, the groups thus being scanned cyclically in a complete cycle of 1,000 time positions, in which the time position of an impulse characterizes both the number of the outlet and the group to which it belongs. Tube ET1, being connected as a cathode follower, repeats the impulses over wire V to the selectors and thence over wires d to the register-controllers. Tube AT (Fig. 2) converts these impulses into positive impulses which are then applied to the grid of RT1, to which are also applied positive impulses derived from one of the sources Pd connected up by the digital register (not shown), and short positive impulses from a source DI producing an impulse in every Pa time position slightly staggered behind the starting time of the Pa impulses. When all three impulses coincide, tube RT1 is triggered and causes tube RT2 in conjunction with transformer TP, TS and thermistor VS to produce a rectangular impulse (the amplitude and duration of which are independent of those of the trigger impulse) which is applied to cold cathode tubes Va1... 5, Vb1 ... 5, Vc1 . . . 4, Vd. The tubes Va; Vb, Vc are each controlled by a pulse source so that an impulse arriving in any time unit will ionize a combination of one particular tube in each group Va, Vb, Vc, as well'as tube Vd. This combination characterizes the time unit, and the tubes hold over their anode circuits via corresponding anode relays. The firing of Vd changes the potential of potential divider DPT so that the grid potential of suppressor tube ST, and thus its cathode potential and that of RT1, are changed to prevent RT1 from responding to further impulses. F (Fig. 2) pulls up in series with Vd  and short-circuits B which being sluggish remains up long enough for test relay T to be connected to wire a to test the availability of the common control circuit. If the common control circuit is not effecting a connection over another selector, T operates and shunts its high resistance winding by its low resistance winding in series with Dt, thus busying the common control circuit. Dt pulls up and disconnects B which then falls away at once. The operated tubes and anode relays hold in series with U, which operates followed by V. The operated anode relays connect the pulse sources Ra, Rb and Rc, which together characterize the outlet selected to a gate system connected to the grid of tube BT (Fig. 2) so that this grid becomes relatively positive in the corresponding time unit and its cathode supplies a positive impulse to wire c. In the common control circuit this impulse results in the firing of one tube in each of the groups VRA, VRB, VRC and the operation of the corresponding anode relays to record its time position. The first two sets of relays Ara ... Are, and Bra.... Bre determine which vertical magnet VM, and the third set Cra .... Crd which vertical servo-magnet shall be operated. In addition Cra ... Crd, also determine whether GD or GE shall be operated. GF (Fig. 5) also operates, short-circuits GB which being sluggish holds up, and disconnects the test potential from wire VI to release T and Dt (Fig. 2). The resulting operation of OK (Fig. 2) restores, the fired tubes, the anode relays and relay U, whereupon V commences to fall off but remains up long enough to permit T and Dt to make another test. OK also disconnects ground from wire b so that GA (Fig. 4) holds in series with magnet HM to the ground on wire e. The changeover of the contacts of HM completes a circuit for T (Fig. 2) over back U and front V to wire VII, relay GC, front GD or GE and one of the vertical bar contacts VBA, or VBB to the wire e<SP>1</SP> of the outlet selected. If the outlet is free, T and Dt operate in turn to the battery on wire e<SP>1</SP> and busy the outlet for D.C. testing and to the scanning cir